As the tray used in the sintering of cermets at a temperature of 1300 to 1500° C., JP-A 2000-509102 discloses a tray in which a substrate of graphite is coated with Y2O3 containing up to 20% by weight of ZrO2. The tray of this patent publication has the problem that reaction can take place between yttrium oxide and graphite at elevated temperatures of 1500° C. or higher or in a reducing atmosphere to partially form yttrium carbide, inviting a reduced mechanical strength and a stripping likelihood. Then it was also proposed to form an interlayer of at least one element of Mo, W, Nb, Zr and Ta between yttrium oxide and graphite for inhibiting the reaction therebetween. However, the provision of the interlayer requires additional steps and increased costs. It is also a problem that graphite tends to adsorb airborne moisture and carbon dioxide gas and release the once adsorbed moisture and gas in vacuum.